[ARM] omap: i2c: remove conditional ick clocks

By providing a dummy ick for OMAP1510 and OMAP310, we avoid having
SoC conditional clock information in i2c-omap.c.  Also, fix the
error handling by making sure we propagate the error returned via
clk_get().

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>