clk: qcom: Constify struct pll_vco

pll_vco structure are never modified. They are used as .vco_table in
"struct clk_alpha_pll".

And in this structure, we have:
	const struct pll_vco *vco_table;

Constifying these structures moves some data to a read-only section, so
increase overall security.

On a x86_64, with allmodconfig:
Before:
   text	   data	    bss	    dec	    hex	filename
   9905	  47576	      0	  57481	   e089	drivers/clk/qcom/mmcc-msm8994.o

After:
   text	   data	    bss	    dec	    hex	filename
  10033	  47440	      0	  57473	   e081	drivers/clk/qcom/mmcc-msm8994.o

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Link: https://lore.kernel.org/r/c3c9a75ed77a5ef2e9b72081e88225d84bba91cd.1715359776.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Bjorn Andersson <andersson@kernel.org>