staging: sm750fb: change default screen resolution

The previous patch which updated screen resolution was tested under
wrong environment. sm750 driver does not support 24bpp. It only
supports 8bpp, 16bpp and 32bpp.
Lets update the default screen resolution to use 32bpp for a better
screen performance.

Fixes: ac669251 ("staging: sm750fb: change default screen resolution")
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>