drivers: core: use strcmp when find device by name

drivers: core: use strcmp when find device by name

`if (!strncmp(dev->name, name, strlen(name)))` might find out
the wrong device, it might find out `dram_pll_ref_sel`, when name is
`dram_pll`. So use strcmp to avoid such issue.

Signed-off-by: Peng Fan <[email protected]>
Reviewed-by: Simon Glass <[email protected]>
Reviewed-by: Bin Meng <[email protected]>