clk: palmas: Add a missing SPDX license header

Add the missing SPDX license header to drivers/clk/clk-palmas.c.

Signed-off-by: Jason Wang <wangborong@cdjrlc.com>
Link: https://lore.kernel.org/r/20210731132226.424853-1-wangborong@cdjrlc.com


[sboyd@kernel.org: Also remove boilerplate from comment]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>