ARM: OMAP2: Set PRCM_CLKSRC_CTRL correctly in omap2_enable_osc_ck

This patch fixes an incorrect use of prm_rmw_reg_bits() in
omap2_enable_osc_ck() which is changing bits in PRCM_CLKSRC_CTRL
that are unrelated to the function it is performing.

Signed-off-by: Seth Forshee <seth.forshee@gmail.com>
Acked-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>