clk: clk-xgene: simplify if-if to if-else

clk: clk-xgene: simplify if-if to if-else

Replace `if (!pclk->param.csr_reg)` with `else` for simplification
and add curly brackets according to the kernel coding style:

"Do not unnecessarily use braces where a single statement will do."

...

"This does not apply if only one branch of a conditional statement is
a single statement; in the latter case use braces in both branches"

Please refer to:
https://www.kernel.org/doc/html/v5.17-rc8/process/coding-style.html

Signed-off-by: Yihao Han <hanyihao@vivo.com>
Link: https://lore.kernel.org/r/20220408130617.14963-1-hanyihao@vivo.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>