ARM: OMAP2+: mux: correct wrong error messages

This is needed because the omap_mux_get_by_name()
function calls the _omap_mux_get_by_name subfunction
for each mux partition until needed mux is not found.
As a result, we get messages like
"Could not find signal XXX" for each partition
where this mux name does not exist.

This patch fixes wrong error message in
the _omap_mux_get_by_name() function moving it
to the omap_mux_get_by_name() one and as result
reduces noise in the kernel log.

My kernel log without this patch:
[...]
[    0.221801] omap_mux_init: Add partition: #2: wkup, flags: 3
[    0.222045] _omap_mux_get_by_name: Could not find signal fref_clk0_out.sys_drm_msecure
[    0.222137] _omap_mux_get_by_name: Could not find signal sys_nirq
[    0.222167] _omap_mux_get_by_name: Could not find signal sys_nirq
[    0.225006] _omap_mux_get_by_name: Could not find signal uart1_rx.uart1_rx
[    0.225006] _omap_mux_get_by_name: Could not find signal uart1_rx.uart1_rx
[    0.270111] _omap_mux_get_by_name: Could not find signal fref_clk4_out.fref_clk4_out
[    0.273406] twl: not initialized

[...]

My kernel log with this patch:
[...]
[    0.221771] omap_mux_init: Add partition: #2: wkup, flags: 3
[    0.222106] omap_mux_get_by_name: Could not find signal sys_nirq
[    0.224945] omap_mux_get_by_name: Could not find signal uart1_rx.uart1_rx
[    0.274536] twl: not initialized
[...]

Signed-off-by: Ruslan Bilovol <ruslan.bilovol@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>