staging: sm750fb: Remove an unnecessary local variable in a function

Remove an unnecessary local variable in  sm750_format_pll_reg function
and replace its initialization directly in return type.
Issue suggested by Coccinelle using ret.cocci.

Signed-off-by: Madhumitha Prabakaran <madhumithabiw@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>