swresample/arm: remove unintentional relocation.

Branch to global symbol results in reference to PLT, and when compiling
for THUMB-2 - in a R_ARM_THM_JUMP19 relocation. Some linkers don't
support this relocation (ld.gold), while others can end up truncating
the relocation to fit (ld.bfd).

Convert this branch through PLT into a direct branch that the assembler
can resolve locally.

See https://github.com/android-ndk/ndk/issues/337 for background.

The current workaround is to disable neon during gstreamer build,
which is not optimal and can be reverted after this patch:
https://github.com/freedesktop/gstreamer-cerbero/commit/41556c415739fbc3a72c7eaee7e70a565b719b2fSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>

libswresample/arm/audio_convert_neon.S

@@ -22,6 +22,7 @@
 #include "libavutil/arm/asm.S"
 
 function swri_oldapi_conv_flt_to_s16_neon, export=1
+_swri_oldapi_conv_flt_to_s16_neon:
         subs            r2,  r2,  #8
         vld1.32         {q0},     [r1,:128]!
         vcvt.s32.f32    q8,  q0,  #31
@@ -66,6 +67,7 @@ function swri_oldapi_conv_flt_to_s16_neon, export=1
 endfunc
 
 function swri_oldapi_conv_fltp_to_s16_2ch_neon, export=1
+_swri_oldapi_conv_fltp_to_s16_2ch_neon:
         ldm             r1,  {r1, r3}
         subs            r2,  r2,  #8
         vld1.32         {q0},     [r1,:128]!
@@ -133,8 +135,8 @@ function swri_oldapi_conv_fltp_to_s16_nch_neon, export=1
         cmp             r3,  #2
         itt             lt
         ldrlt           r1,  [r1]
-        blt             X(swri_oldapi_conv_flt_to_s16_neon)
-        beq             X(swri_oldapi_conv_fltp_to_s16_2ch_neon)
+        blt             _swri_oldapi_conv_flt_to_s16_neon
+        beq             _swri_oldapi_conv_fltp_to_s16_2ch_neon
 
         push            {r4-r8, lr}
         cmp             r3,  #4