platform_data/mlxreg: mlxreg.h: fix all kernel-doc warnings

Use the correct kernel-doc format & notation to eliminate
kernel-doc warnings:

Warning: include/linux/platform_data/mlxreg.h:24 Enum value
 'MLX_WDT_TYPE1' not described in enum 'mlxreg_wdt_type'
Warning: include/linux/platform_data/mlxreg.h:24 Enum value
 'MLX_WDT_TYPE2' not described in enum 'mlxreg_wdt_type'
Warning: include/linux/platform_data/mlxreg.h:24 Enum value
 'MLX_WDT_TYPE3' not described in enum 'mlxreg_wdt_type'
Warning: include/linux/platform_data/mlxreg.h:37 bad line:
 PHYs ready / unready state;
Warning: include/linux/platform_data/mlxreg.h:153 struct member 'np'
 not described in 'mlxreg_core_data'
Warning: include/linux/platform_data/mlxreg.h:153 struct member 'hpdev'
 not described in 'mlxreg_core_data'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://patch.msgid.link/20260226051232.549537-1-rdunlap@infradead.org
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>