clk: gate: fix comment typo and grammar

Change ouput -> output.

While at it change also grammatically incorrect "it's" to "its".

Signed-off-by: Baruch Siach <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Stephen Boyd <[e-mail]>

drivers/clk/clk-gate.c

···
 #include <linux/string.h>
 
 /**
- * DOC: basic gatable clock which can gate and ungate it's ouput
+ * DOC: basic gatable clock which can gate and ungate its output
  *
  * Traits of this clock:
  * prepare - clk_(un)prepare only ensures parent is (un)prepared