ARM: use 2-operand syntax for ADD Rd, PC in Apple PIC code

The Apple assembler refuses to assemble the 3-operand form
in Thumb2 even though it is valid syntax.

Signed-off-by: Mans Rullgard <mans@mansr.com>

libavutil/arm/asm.S

@@ -143,7 +143,7 @@ ELF     .size   \name, . - \name
     .if \indir
         ldr             \rd, [pc, \rd]
     .else
-        add             \rd, \rd, pc
+        add             \rd, pc
     .endif
         def_pic         \val - (.Lpic\@ + (8 >> CONFIG_THUMB)), .Lpicoff\@
 .endm