arm: Avoid using the movw instruction needlessly

This fixes building for ARM11 without Thumb2.

Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/arm/ac3dsp_armv6.S

@@ -37,7 +37,7 @@ function ff_ac3_bit_alloc_calc_bap_armv6, export=1
         ldrb            r10, [r4], #1
 1:
         ldrsh           r9,  [r0], #2                   @ mask[band]
-        movw            r8,  #0x1fe0
+        mov             r8,  #0xff0
         sub             r9,  r9,  r12                   @   - snr_offset
         mov             r11, r10
         ldrb            r10, [r4], #1                   @ band_start_tab[band++]
@@ -45,7 +45,7 @@ function ff_ac3_bit_alloc_calc_bap_armv6, export=1
         it              lt
         movlt           r9,  #0
         cmp             r10, r3                         @   - end
-        and             r9,  r9,  r8                    @   & 0x1fe0
+        and             r9,  r9,  r8, lsl #1            @   & 0x1fe0
         ite             gt
         subgt           r8,  r3,  r11
         suble           r8,  r10, r11