drm/omap: fix align_pitch() for 24 bits per pixel

align_pitch() uses ALIGN() to ensure the pitch is aligned to SGX's
requirement of 8 pixels. However, ALIGN() expects the alignment value to
be a power of two, which is not the case for 24 bits per pixels.

Use roundup() instead, which works for all alignments.

This fixes the error seen with 24 bits per pixel modes:

"buffer pitch (2176 bytes) is not a multiple of pixel size (3 bytes)"

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>