drm: mali-dp: Mark expected switch fall-through

drm: mali-dp: Mark expected switch fall-through

Now that -Wimplicit-fallthrough is passed to GCC by default, the
following warnings shows up:

../drivers/gpu/drm/arm/malidp_hw.c: In function ‘malidp_format_get_bpp’:
../drivers/gpu/drm/arm/malidp_hw.c:387:8: warning: this statement may fall
 through [-Wimplicit-fallthrough=]
    bpp = 30;
    ~~~~^~~~
../drivers/gpu/drm/arm/malidp_hw.c:388:3: note: here
   case DRM_FORMAT_YUV420_10BIT:
   ^~~~
../drivers/gpu/drm/arm/malidp_hw.c: In function ‘malidp_se_irq’:
../drivers/gpu/drm/arm/malidp_hw.c:1311:4: warning: this statement may fall
 through [-Wimplicit-fallthrough=]
    drm_writeback_signal_completion(&malidp->mw_connector, 0);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../drivers/gpu/drm/arm/malidp_hw.c:1313:3: note: here
   case MW_START:
   ^~~~

Rework to add a 'break;' in a case that didn't have it so that
the compiler doesn't warn about fall-through.

Cc: stable@vger.kernel.org # v5.2+
Fixes: b8207562abdd ("drm/arm/malidp: Specified the rotation memory requirements for AFBC YUV formats")
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190730153056.3606-1-anders.roxell@linaro.org