DRM: ast: Fixed coding style issues of ast_mode.c

Removed space before comma, fixed if statements by putting trailing
statements on new line, fixed unsigned int declaration, and removed
not needed else statement after return.

Signed-off-by: Gregory Williams <gregwills85@gmail.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20210731005328.GA19016@devbox