In the mentioned situation, the Salaah will be valid. However, if a person reads less than the required Tasbih of a certain posture, he may complete it in the next posture. For example: If he reads less than the required amount in the first Sajdah, he may complete it in the second Sajdah. It is appropriate that one should abstain from completing the missed Tasbihs in the Qaumah(the posture after Ruku) and Jalsah(the posture after the first Sajdah). There will be no Sajdah-Sahwa for this omission. (Shaami 2/27).