clk: at91: utmi: use pmc_read when the at91_pmc is available

at91_pmc_read is a workaround to allow external drivers to acces some
registers of the PMC. There is no need for it in clk-utmi.c as we aready
have a pointer to the struct at91_pmc.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>